In the case of an optical code reader, the processing of the acquired image makes it possible to identify the characteristics of the elements of the code, such as the width and/or the number of bands and spaces in the case of barcodes or stacked codes, the magnitude of two-dimensional elements in the case of two-dimensional codes, the colour in the case of colour codes, etc. Such characteristics encode the most widely varying information associated with any object carrying the optical code.
Just as an example, in the fields of transportation, of delivery and of storage of goods, optical codes make it possible to easily keep track of goods.
Similarly, in artificial vision and inspection systems an area is illuminated and an image thereof is acquired for its remote display or for the most widely varying subsequent processing, according to the intended purpose.
In such image acquisition devices it is necessary to illuminate the entire width of a 1D code or an entire 2D code, or more generally the entire area of which an image is to be acquired, and to collect and detect the light diffused by the code or by the area through a suitable photodetector device or sensor.
Image acquisition devices have different critical aspects.
Both in the one-dimensional case and in the two-dimensional case, the performance of an image acquisition device is optimal only within a certain depth of field, meant as the range of distances between the image acquisition device and the optical code or the area of which the image is to be acquired.
The acquisition distance can, however, change greatly according to the intended application, or even within the same application, as the conditions change.
The depth of field depends greatly upon the receiving optics of the image acquisition device and is affected by the sources and by the optics for illuminating the area to be acquired.
In order to increase the depth of field, autofocus devices are known that typically provide for electromechanical movement of parts of the optics. Such autofocus devices substantially increase the bulk, the weight, the cost, and the complexity of image acquisition devices.
It has also been proposed to provide for acquisition devices with two different acquisition subsystems, having depths of field centered at different distances, so that the overall depth of field of the acquisition device results from the juxtaposition of the two depths of field. Practical embodiments of such acquisition devices, however, provide for use of various optical components for forming two suitable illumination patterns and for imaging on two sensors, as well as of mirrors for deflecting the collected light onto the two sensors, also in this case substantially increasing the bulk, the weight, the cost and the complexity of image acquisition devices.
In image acquisition systems it is essential to ensure a predetermined mutual positioning or alignment in the broadest sense that is very precise between all of the optical, mechanical and optoelectronic components in order to make performance optimal. It follows from this that, if the number of components to be assembled substantially increases, the production and/or installation cost increases proportionally.
In particular, in the case of portable, hand-held or wearable, for example wrist- or finger-wearable image acquisition devices, the weight and bulk must be kept particularly low to allow a prolonged use thereof. Acquisition devices weighing from 50 g to 100 g and with size of about 50-70 mm×50-70 mm×50-70 mm, like those currently on the market, are tiring and therefore not very ergonomic.
Then in the case of complex portable or fixed processing systems, the image acquisition is often associated with other optoelectronic functions, including the projection of a luminous aiming figure, used for the correct positioning of the device with respect to the area from which the image is to be acquired; the projection of a luminous outcome figure, i.e. indicative of the positive or negative outcome and of possible reasons for negative outcome of the acquisition and/or processing of the image and/or decoding in the case of an optical code reader; the optoelectronic detection of presence of an image to be acquired, in particular of an optical code, in the field of view of the acquisition device; the optoelectronic distance measurement, to provide feedback on the position of the image to be acquired with respect to the acquisition device, possibly through triangulation; the transmission, reception or transmission/reception of information, for example for the transmission of the acquired image, or of a processed version thereof, to an external device.
All or part of these functions can be carried out by exploiting electromagnetic radiation with continuous spectrum or with different wavelengths and selected in suitable ranges, according to the intended purpose.
Such functions require the use of additional optoelectronic subsystems, which leads to an increase in the number of optical components to be assembled, as well as to an increase in weight and bulk of the image acquisition device if integrated in it. Vice-versa, should the aforementioned subsystems not be integrated into the image acquisition device, the space available for the latter can in any case be extremely small.
The technical problem at the basis of the present invention is to provide an image acquisition device and an optical component thereof that provide good performance and versatility with respect to one or more of the aforementioned requirements, in particular that are particularly compact and light and simple to assemble, in particular intrinsically capable of ensuring the correct mutual positioning of the different optical, mechanical and optoelectronic components.